1. Technical Field of the Invention
The present invention relates to test mode circuitry, and more particularly to test mode circuitry useful in connection with a programmable tamper detection alarm circuit.
2. Description of Related Art
There exist electronics systems in which very sensitive data may be stored in an integrated circuit (IC). For example, some portable credit card scanners store credit card data in volatile memory which, if pilfered, would potentially expose credit card holders to credit card fraud.
In an effort to prevent such pilfering of data, techniques exist for detecting when an IC or system is being tampered with, and destroying the stored data in response to the detection. In this way, sensitive data stored in such systems remains inaccessible.
It is also known to custom program an integrated circuit for a given customer. In connection with a tamper detection integrated circuit, the programmed threshold voltage(s) which would trigger an alarm from the circuit could differ among the customers for that integrated circuit. If the custom programming for one customer differs from that of another customer, it is critical that the produced integrated circuits for the two customers do not get mixed up with other. There is accordingly a need for a mechanism to test a programmed integrated circuit to ensure it belongs to a given customer.
It is also known in the art with respect to tampering of integrated circuits for the tamperer to enter the test mode of the integrated circuit in order to try and access information or circuit outputs. A need accordingly exists for circuitry that would impede a tamperer's access to stored information or certain circuit outputs when the integrated circuit is placed in test mode.